1. Field of the invention
The present invention relates to an organic electroluminescence (EL) display device, more particularly, to an organic EL display device in which an opening ratio is improved by extending an emission region to between wirings.
2. Discussion of the Background
Various thin, light weight flat panel displays, including liquid crystal displays, field emission displays, plasma display panels, and organic EL display devices, are being developed to replace cathode ray tubes.
Organic EL display devices are receiving increasing attention since they may be driven by a low DC voltage and they have a fast response speed.
The organic EL display device may be a passive matrix or active matrix type display device. Generally, the active matrix type organic EL display device drives light-emitting elements by arranging a switching element at each pixel. FIG. 1 is a plan view showing a conventional active matrix type organic EL display device.
Referring to FIG. 1, a plurality of data lines 11 (D1 . . . DZ), which transfer data signals, are connected to a data driver 10, and a plurality of scan lines 21 (S1 . . . SY), which transfer selection signals, are connected to a scan driver 20. A display panel 30 comprises a plurality of unit pixels 40 formed near crossings of the data lines 11 and the scan lines 21.
The data driver 10 and the scan driver 20 output data signals and selection signals to the unit pixels 40 through the data lines 11 and the scan lines 21, respectively, and applying a data signal to a unit pixel 40 lights that pixel so that the display panel 30 displays a certain image.
FIG. 2 is a cross-sectional view showing a unit pixel 40 in a conventional bottom-emission type organic EL display device.
As shown in FIG. 2, a conventional unit pixel 40 may comprise a buffer layer 43b formed on an insulating substrate 43a, a switching thin film transistor (TFT) 41 and a driving TFT 42 formed on the buffer layer 43b, and a passivation layer 44 formed on the switching and driving TFTs 41 and 42. An anode electrode 46 is formed on the passivation layer 44 and coupled to a drain electrode 42a of the driving TFT 42. A pixel defining layer 45 is formed on the passivation layer 44 and the anode electrode 46 with an opening part 50 exposing a part of the anode electrode 46. An organic thin film layer 47 is formed on an upper part of the pixel defining layer 45 and the exposed anode electrode 46, and a cathode electrode 48 is formed on an upper surface of the organic thin film layer 47.
A bump may be generated on the passivation layer 44 by a bump generated during formation of a TFT when using an organic layer as the passivation layer 44. Therefore, the anode electrode 46 may be formed on a flat part of the passivation layer 44 that is not above a TFT.
FIG. 3 is a plan view showing a unit pixel in a conventional organic EL display device.
Applying selection signals to the switching TFT 41, through the scan line 21, turns it on to transfer data signals from the data line 11 to a capacitor 51, so that the capacitor 51 may store the data signals and transfer the stored data signals to the driving TFT 42. The driving TFT 42 transfers driving current, corresponding to the data signals and applied through a power supply voltage line 52, to the anode electrode 46 so that the anode electrode 46, organic thin film layer 47 and cathode electrode 48 operate to emit light through the opening part 50.
However, the conventional bottom-emission type organic EL display device may have a small opening ratio because each unit pixel is divided into a wiring region comprising a plurality of wirings, the switching TFT, the driving TFT, and an emission region for emitting light. Hence, displayed images may not be smooth, and image quality may deteriorate as an emitting part and a dark part coexist in each pixel since a space between the wirings of the wiring region is dark even when the emission region is lit. A double-sided organic EL display device may also have deteriorated display quality because a luminance difference between the top and bottom of the device may increase.